Method and instrument for tensioning a flexible tie

ABSTRACT

A method and instrument for tensioning a flexible tie used for fastening an implant on a bony element by forming a first loop around it. In some embodiments, the instrument comprises a shaft having a distal end configured for contact with a rod, a moving part slidably engaged with the shaft, a holder connected to the moving part and configured to hold an end of the flexible tie, and a tension control member comprising a trigger that pivots relative to the moving part. In some embodiments, the method comprises coupling the end of the flexible tie to the instrument and squeezing the trigger to shorten the first loop of the flexible tie around the bony element, causing the moving part and the holder holding the end of the flexible tie to move in translation away from the distal end of the shaft, thereby exerting tension on the flexible tie.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims a benefit of priorityunder 35 U.S.C. §120 from U.S. patent application Ser. No. 12/408,592,filed Mar. 20, 2009, entitled “FLEXIBLE TIE FASTENING SYSTEM,” which isa continuation of and claims priority from U.S. patent application Ser.No. 11/996,918, filed Jan. 25, 2008, entitled “AN INSTRUMENT FORTENSIONING A FLEXIBLE TIE,” which is the National Stage of InternationalApplication No. PCT/FR2006/050909, filed Sep. 20, 2006, which claimspriority from French Patent Application No. 0509629, filed on Sep. 21,2005. This application also relates to U.S. patent application Ser. No.13/154,257, filed Jun. 6, 2011, entitled “SPINAL IMPLANT WITH FLEXIBLETIE.” The content of each application referenced herein is herebyincorporated as if fully set forth herein.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method and instrument for tensioning aflexible tie used for fastening an implant on a bony element by forminga first loop around the bony element.

BACKGROUND OF THE RELATED ART

The spine is made up of a superposition of vertebrae, that are normallyaligned along a vertebral axis, going from the lumbar vertebrae to thecervical vertebrae, with each vertebra presenting a posterior wall fromwhich there projects a spinous process and two side edges having wallsfrom which there project the ribs and/or transverse processes. When anindividual's spine presents abnormal curvature, the vertebrae areinclined relative to one another and relative to said vertebral axis.The lateral edges of the vertebrae situated on one side are thus closerto one another and form a concave curve, while the lateral edges on theother side appear spaced apart from one another and form a convex curve.

In order to straighten the spinal column, the lateral edges of thevertebrae on the concave side are spaced apart from one another and aretaken relative to one another to a distance that is substantiallyequivalent to the distance between the lateral edges on the other side.Thereafter, in order to keep the vertebrae in that position relative toone another, known devices are used that have screws for insertion intothe vertebrae or hooks for inserting along the inside wall of the spinalcanal, associated with rods for interconnecting the screws or the hooks.

SUMMARY OF THE INVENTION

The hooks are generally inserted in pairs in each vertebra and on eitherside close to the pedicles, the heads of the hooks projecting from theposterior wall of a vertebra, one on either side of the spinous process.The heads may be tulip-shaped, for example, and they are suitable forreceiving a rod which is secured by means of a nut screwed onto the headand bearing against the rod. Rows constituted by the heads of the hookssituated on either side of the spinous processes are interconnected andheld in fixed position by two rods that are parallel to each other andto the axis of the spine.

Nevertheless, using such hooks is tricky, since under no circumstancesmust the operator harm the spinal cord that extends in the center of thespinal canal, since that would lead to paralysis for the patient.

The use of screws makes it possible to reduce the risks of such surgery.They likewise have tulip-shaped heads and they are inserted in pairs inthe posterior walls of vertebrae in the pedicles on either side of thespinous processes. Thus, the screws constitute fastening points in thevertebrae for holding them relative to one another. Nevertheless, thescrews are necessarily inserted into the pedicles of the vertebrae, andunder certain circumstances, the pedicles may be small in size or theymay be damaged.

A problem which arises, and which the invention seeks to solve, is howto obtain such fastening points when it is not possible to introducescrews into the vertebrae in the curved portion, and when using hookswould be too dangerous.

In PCT patent application WO 2004/010881 in the name of the Applicant, avertebral fastener system is described that enables this problem to besolved.

That vertebral fastener system suitable for mounting on a vertebra ofthe spine for connection to a rod comprises:

-   -   a connection piece disposed facing said rib and/or said        transverse process, and suitable for being connected to said        rod;    -   a flexible tie of elongate shape suitable for connecting        together said connection piece and at least one rib and/or        transverse process; and    -   adjustable locking means secured to said connection piece, said        tie presenting a first end secured to said connection piece and        a free second end suitable for sliding in said connection piece        and to form a loop, said locking means being suitable for        simultaneously holding said connection piece in a fixed position        relative to the rod and a portion of said tie extending between        said ends being suitable for being locked in translation        relative to said connection piece by said adjustable locking        means, whereby the loop presents a length that is determined in        such a manner as to prevent relative displacement of said rod        and of said vertebra in opposite directions.

Other flexible tie systems for fastening to a vertebra can be used. Thisapplies in particular to the system shown in accompanying FIG. 1.

It comprises a connection piece 12 constituted by two jaws 20 and 22that are hinged together at one end about an axis 24. The two jaws haverecesses enabling a rod 18 to be put into place and allowing a braid ortie 14 to pass through, the tie forming a loop 28 on one side of theconnection piece 12 and two free ends 30 and 32 on the other side ofsaid piece. The connection system also has a locking member constitutedby a screw 16 that can be engaged in the ends of the jaws 20 and 22remote from their hinged ends. The portions of the tie 14 that areengaged in the recesses are secured to the connection piece by beingpinched between the walls of the recesses in the connection piece andthe rod 18 when the locking screw 16 is fully tightened.

It can be understood that in order to ensure that said assembly isproperly fastened on a transverse process, on a rib, or on a portion ofthe posterior arc of a vertebra, it is necessary to exert tension on thefree ends 30 and 32 of the tie 14.

It will also be understood that with the first-described fastenersystem, it is also necessary to exert tension on the single free end ofthe tie in order to ensure correct fastening on the bony element.

U.S. Pat. No. 5,964,769 discloses a device serving to exert tension on acable used for fastening a medical device on a bone. That devicepresents the drawbacks of acting directly on the tie-tightening deviceand no disposition allows the tension exerted on the tie to becontrolled.

An object of the invention is to provide an instrument for tensioning aflexible tie of an implant that ensures that it is tensioned effectivelywhile nevertheless being easy for the surgeon to use.

To achieve this object, the invention provides an instrument fortensioning a flexible tie used for fastening an implant onto a bonyelement of a patient by forming a first loop around the bony element,said tie presenting at least one end that projects out from saidimplant, and said instrument comprises:

-   -   a rod having a first end provided with bearing means for bearing        against said implant;    -   a moving part that is movable in translation and that surrounds        said rod over a fraction of its length;    -   holder means for holding the end of said tie, said holder means        being connected to said moving part by a dynamometer system; and    -   control means mounted on said moving part to cause the moving        part to move relative to said rod, thereby tending to move the        first end of the rod away from said moving part, thereby        exerting tension on said tie relative to said implant.

It will be understood that since the rod bears against the implant, themoving part is secured either to the second loop of the tie, or to thefree end of said tie serves to exert tension on said tie, therebyensuring appropriate tightening of the first loop of the tie on the bonyelement.

In addition, when the surgeon acts on the control means, the surgeonknows when the appropriate tension has been applied, thus making itpossible to avoid untimely breaking of the tie or damage to the bonyelement.

Preferably, the instrument further comprises an anti-return system fortemporarily preventing said rod and said moving part moving intranslation relative to each other, in the absence of action on thecontrol means.

Preferably, the dynamometer system comprises a carriage that is movablein translation relative to the rod and to the moving part, saidtie-holder stud being secured to said carriage, and a compression springbeing interposed between said carriage and a portion of the moving part.

Also preferably, the control means comprise a trigger mounted to pivotrelative to the moving part and presenting a manual actuator portion anda finger that acts on said rod.

Also preferably, the instrument further comprises a handle secured tosaid moving part and disposed in such a manner that the user can graspsaid trigger and said handle simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention appear better onreading the following description of an embodiment of the inventiongiven by way of non-limiting example. The description refers to theaccompanying figures, in which:

FIG. 1, described above, shows an example of an implant with a fastenertie with which the instrument of the invention can advantageously beused;

FIG. 2 is a perspective view of the instrument assembly of theinvention;

FIG. 3 is an exploded view of the disassembled instrument showing itsinternal mechanisms; and

FIG. 4 is a perspective view showing the instrument in use with animplant of the type shown in FIG. 1.

DETAILED DESCRIPTION

With reference initially to FIG. 2, there follows a description of theinstrument assembly 40. It is essentially constituted by a rod 42 havinga first end 42 a fitted with bearing means 44 for bearing against theimplant on which the tie is to be tensioned. The instrument 40 also hasa moving part 46 that is movable in translation relative to the rod 42.The moving part 46 is generally cylindrical in shape and is providedwith a handle 48. The moving part 46 also has a stud 50 on its portionremote from the handle 48. As explained below, the stud 50 serves tohold the tie on which tension is to be applied. The instrument 40 alsocomprises a control member constituted by a trigger 52. As explainedbelow, actuating the trigger 52 serves to cause the moving part 46 tomove rearwards relative to the rod 42 in the direction of arrow F. Inaddition, at its end 46 a opposite from its end 46 b closest to thebearing element 44, the moving part 46 is fitted with an anti-returnsystem acting on the rod 42. As explained in greater detail below, theanti-return system 54 enables the rod 42 and the moving part 46 to beheld together temporarily in translation so long as no action is exertedon the trigger 52.

With reference more particularly to FIG. 4, there follows a descriptionin general terms of how the instrument 40 is used. In this figure, therecan be seen a vertebral fastener system 10 of the type shown in FIG. 1.In this figure, there can be seen the rod 18, the connection piece 12,and the first fastener loop 28 formed by the tie 14 of the fastenersystem. This figure also shows that the free end 32 of the tie 14 isconnected to the other free end 30 of the same tie by a fastener element55 of suitable type. Thus, the tie 14 forms a second loop 56.

In use, the bearing means 44 of the instrument bear against the rod 18on either side of the connection piece 12. The second loop 56 of the tie14 is engaged on the stud 50 of the moving part 46 of the instrument. Itwill be understood that when the surgeon exerts action by using thetrigger 52 and the handle 48, this causes the moving part 46 to movebackwards in the direction F relative to the rod 18, thereby applyingtraction to the tie as a whole, and in particular to its loop 28. Thesurgeon can exert successive actions on the trigger 52 because of thepresence of the anti-return system 54. As explained below, theinstrument is preferably also fitted with a dynamometer system thatenables the surgeon to see when a suitable tension has been exerted onthe tie 14. Once the suitable tension has been exerted, the instrument40 is separated from the loop 56 in the tie 14, and the portions of thetie 14 that project beyond the connection piece 12 are cut off.

With reference to FIG. 3, there follows a description in greater detailof the mechanisms of the instrument 40. This figure shows thecylindrically-shaped moving part 46 on which the handle 48 is secured.The trigger 52 is hinged relative to the handle 48 about a pin 60. Thetrigger 52 has a grip portion 52 a and a finger 52 b for controlling therod 42, for which finger 52 b projects beyond the pivot pin 60. Thefinger 52 b penetrates into the moving part 46 via a slot (not shown).The rod 42 is slidably engaged in the moving part 46.

Various elements that are described below are mounted around the rod 42inside the moving part 46 having open ends that are closed by endpieces62 and 64 each pierced by an axial bore for passing the rod 42. A spring66 and a plate 68 constituting the anti-return system are mountedoutside the moving part 46, around the rod 42. The plate 68 is piercedby a bore 70 of diameter that is slightly greater than the diameter ofthe rod. The plate 68 has a tongue 72 that can bear against an arm 74secured to the rear portion of the moving part 46. Inside the movingpart 46 and starting from its end closed by the endpiece 64, there is aspacer cylinder 76, a transmission part 78 constituted by an annularportion 78 a and by a stud 78 b suitable for co-operating with thefinger 52 b of the trigger 52. The transmission part 78 is associatedwith a spring 80. Thereafter there is a carriage 82 having a cylindricalportion 82 a engaged around the rod 42 and two external projections 82b. The projections 82 b of the carriage 82 are external to the movingpart 46 by virtue of a longitudinal slot 84 therein. This externalportion of the carriage 82 has the tie-holding stud 50 secured thereto.The carriage 82 is associated with a dynamometer spring 86 which isinterposed between the endpiece 62 and the front face of the cylindricalportion 82 a of the carriage 82.

In the absence of any action on the trigger 52, the plate 68 of theanti-return system slopes relative to the rod 42 because of the presenceof the end 74 a of the arm 74, thus causing the rod 42 and the movingpart 46 to be temporarily secured to each other in translation. Whenaction is exerted on the trigger 52, the movement of the rod releasesthe plate 68 and thus allows the rod 42 to move relative to the movingpart 46. Similarly, when no action is applied to the trigger 52, thetransmission part 78 is free, whereas, in contrast, when action isapplied to the trigger 52, the finger 52 b acts on the stud 78 b of thetransmission part 78, thereby temporarily securing it to the rod 42.This temporary connection serves to move the rod 42 relative to the part46 under the effect of the trigger being actuated.

The dynamometer system operates in simple manner. Under the effect ofthe rod 42 moving in the direction F relative to the part 46, thedynamometer spring 86 is compressed, causing the carriage 82 to performrelative movement. A mark on the outside face of the moving part 46makes it possible to detect when the appropriate tension has beenapplied, this tension corresponding naturally to the dynamometer spring86 being subjected to predetermined compression.

In the description above, it is assumed that the tie 14 has a secondloop used for holding onto the tensioning stud 50 of the instrument.When the tie of the implant has only one free end, this end can be heldon the stud 50 or on any other appropriate fastener system so as toexert in the same manner the desired tension on the end of the tie andthus on the loop 28 formed thereby.

1. An instrument for tensioning a flexible tie, comprising: a shafthaving a distal end configured for contact with a rod; a moving partslidably engaged with the shaft; a holder connected to the moving partand configured to hold an end of the flexible tie, the holder beingmovable in translation relative to the shaft; and a tension controlmember connected to the moving part and configured to cause the movingpart and the holder holding the end of the flexible tie to move intranslation away from the distal end of the shaft, thereby exertingtension on the flexible tie.
 2. An instrument according to claim 1,wherein the end of the flexible tie held by the holder comprises a freeend of the flexible tie.
 3. An instrument according to claim 1, whereinthe flexible tie comprises a first loop around a bony element andwherein the end of the flexible tie held by the holder comprises asecond loop of the flexible tie.
 4. An instrument according to claim 3,wherein the holder comprises a capture post and wherein the second loopis wrapped around the capture post.
 5. An instrument according to claim4, further comprising: a tension gauge located at a distal end of thecapture post.
 6. An instrument according to claim 5, wherein the tensiongauge comprises an indicator line on an outer surface of the movingpart.
 7. An instrument according to claim 3, wherein translating theholder away from the distal end of the shaft lengthens the second loopof the flexible tie and shortens the first loop of the flexible tiearound the bony element.
 8. An instrument according to claim 1, whereinthe tension control member comprises: a trigger that pivots relative tothe moving part.
 9. An instrument according to claim 8, furthercomprising: an anti-return mechanism for temporarily preventing themoving part and the shaft moving in translation relative to each otherin absence of any action on the trigger.
 10. An instrument according toclaim 8, further comprising: a handle secured to the moving part anddisposed in proximity to the trigger to allow for simultaneous graspingof both the handle and the trigger, wherein the trigger furthercomprises a finger extending into the moving part, and wherein rotatingthe trigger in a first direction relative to the handle engages thefinger of the trigger with the shaft.
 11. An instrument according toclaim 10, wherein further rotation of the trigger in the first directionmoves the moving part in translation away from the distal end of theshaft to tension the flexible tie, and wherein releasing the triggerdisengages the finger from the shaft.
 12. An instrument according toclaim 10, further comprising: a plate having an opening through whichthe shaft is received, the opening of the plate having a diameter thatis slightly greater than a diameter of the shaft; an arm extending fromthe moving part; and a spring, wherein when the trigger is disengagedfrom the shaft the arm biases the plate to a sloped orientation relativeto the shaft to inhibit movement, and wherein when the trigger engagesthe shaft and moves the shaft in the first direction, the spring biasesthe plate into a substantially perpendicular orientation relative to theshaft to enable translational movement of the moving part relative tothe shaft, the shaft being translatable through the opening of theplate.
 13. An instrument according to claim 1, further comprising: amark on an outer surface of the moving part, the mark indicating a levelof tension applied onto the flexible tie.
 14. An instrument according toclaim 13, wherein the level of tension corresponds to a spring beingsubjected to a predetermined amount of compression.
 15. A method fortensioning a flexible tie, comprising: coupling an end of the flexibletie to an instrument, wherein the instrument comprises: a shaft having adistal end configured for contact with a rod; a moving part slidablyengaged with the shaft; a holder connected to the moving part andconfigured to hold the end of the flexible tie, the holder being movablein translation relative to the shaft; and a tension control memberconnected to the moving part, wherein the tension control membercomprises a trigger that pivots relative to the moving part; andgrasping the trigger to cause the moving part and the holder holding theend of the flexible tie to move in translation away from the distal endof the shaft, thereby exerting tension on the flexible tie.
 16. A methodaccording to claim 15, wherein the holder comprises a capture post,wherein the flexible tie comprises a first loop around a bony element,wherein the end of the flexible tie comprises a second loop of theflexible tie, wherein coupling the end of the flexible tie to theinstrument further comprising wrapping the second loop of the flexibletie around the capture post, and wherein translating the capture postaway from the distal end of the shaft lengthens the second loop of theflexible tie and shortens the first loop of the flexible tie around thebony element.
 17. A method according to claim 15, further comprisingreleasing the trigger, wherein the instrument further comprises ananti-return mechanism which temporarily prevents the moving part and theshaft moving in translation relative to each other in absence of anyaction on the trigger.
 18. A method according to claim 15, wherein theinstrument further comprises a handle secured to the moving part anddisposed in proximity to the trigger to allow for simultaneous graspingof both the handle and the trigger, wherein the trigger furthercomprises a finger extending into the moving part, and wherein graspingthe trigger further comprises rotating the trigger in a first directionrelative to the handle to engage the finger of the trigger with theshaft.
 19. A method according to claim 18, wherein grasping the triggerfurther comprises further rotating the trigger in the first direction tomove the moving part in translation away from the distal end of theshaft to tension the flexible tie.
 20. A method according to claim 15,further comprising: verifying a level of tension applied onto theflexible tie via a mark on an outer surface of the moving part.